The present invention relates to a braking system for vehicles equipped with an ABS system or an antiskid protection system.
An antilock system for a motorcycle is known from German Patent Document 39 31 313 A1, in which a total of only two rotational wheel speed sensors are provided, one sensor being assigned to the front wheel and the other being assigned to the rear wheel. For determining the wheel slip, a reference quantity is determined which is approximated to the course of the vehicle speed and in which case two channels are provided. The two reference speeds are determined on the basis of the assigned wheel speed and a multiplier dependent on the driving condition.
U.S. Patent Document U.S. Pat. No. 5,791,744 A describes an electropneumatic braking system for rail vehicles, in which a “universal unit” is assigned to each car and controls the brakes of the respective car. Such a universal unit consists of an electronic portion, a pneumatic portion and an electropneumatic portion. The electronic portion has, among other things, an interface for rotational wheel speed sensors.
German Patent Document DE 198 26 131 A1 describes an electric braking system for a motor vehicle in which two electronic arithmetic channels are provided. In the case of this braking system, among other values, slip values are computed individually for the each wheel. The rotational wheel speed of the respective wheel and a centrally computed estimated value for the vehicle speed are entered into the computation of the slip, the vehicle speed being computed in a single-channel manner, that is, not redundantly.
Modern road and rail vehicles are normally equipped with an antilock system which, in the case of road vehicles, is called an “ABS system” and, in the case of rail vehicles, is called an “antiskid protection system”. ABS systems and antiskid protection systems control the brake pressures at individual wheels or axles of the vehicle such that a locking of the wheels or wheel sets is prevented and the length of the braking path is minimized. For such a brake pressure control, the slip values which exist at the individual wheels or axles are required and are determined from the respective wheel speeds and the actual vehicle speed. For this purpose, rotational wheel speed sensors are normally provided. In which case, an approximate value for the actual vehicle speed, that is, a “reference speed”, is determined from the individual rotational wheel speeds. When the measured rotational wheel speed signals are faulty, for example, as a result of electromagnetic interference fields and/or system-caused measuring errors, which result in “peaks” in the speed course or acceleration course of the measuring signals, errors may then also occur when computing the reference speed.
A “false” reference speed may result in errors in controlling the braking force of the entire vehicle. This is problematic particularly in the case of those vehicles which only have an independent system for the braking force control.
The reason is that ABS systems or antiskid protection systems normally have a single-channel construction; that is, the rotational wheel speeds are detected in a single-channel manner. If one rotational wheel speed sensor fails, the assigned wheels can no longer be controlled corresponding to the existing rotational wheel speed.
To prevent faulty rotational wheel speed signals from falsifying the reference speed value, conventional algorithms for computing the reference speed have a “detection” of faulty signals, but a reliable detection of all possible faults requires very high expenditures. In addition, faults may have an effect on the calculation of the reference speed already during the fault disclosure time such that the braking force control is affected.
It is an object of the invention to provide a braking system which is optimized with respect to the determination of the actual vehicle speed required for an ABS or antiskid protection control. This object is achieved by the present invention.
The basic principle of the invention consists of a braking system with an arithmetic unit which has at least two separate “channels”, in which, independently of one another, a “reference speed” is determined which is approximated to the actual vehicle speed. The at least two reference speeds are in each case used only for controlling a portion of the brakes in the vehicle.
The separate computation of the reference speeds can take place in a brake control unit or in an arithmetic unit. Only a portion of the rotational wheel speed sensors in the vehicle, as well as a portion of the brakes in the vehicle, are assigned to each of the channels. On each channel, rotational wheel speed signals of different sensors are used for computing one reference speed respectively. Consequently, in the case of two channels, maximally half the brakes in the vehicle are controlled on the basis of one of the two reference speeds. Even when only one arithmetic unit, that is, one brake control unit, is provided, an error occurring in the detection of the rotational wheel speed may have an effect on maximally half of the brakes. An individual fault in the speed detection can therefore not influence the entire braking force of the vehicle.
In the “redundant” detection of the rotational wheel speed, at least two rotational wheel speed signals of a wheel or of a wheel group are always included in the control. The wheel or the wheel group can therefore still be controlled when one of the two rotational wheel speed signals fails or has interference. This significantly improves the driving safety.
According to a further development of the invention, for a vehicle or in the case of several vehicle units coupled to one another, including at least one front axle and one rear axle, at least one front axle signal and one rear axle signal is analyzed on each channel. Thus, at least one rotational wheel speed sensor of a front axle and one rotational wheel speed sensor of a rear axle is connected to each channel. The first channel can therefore be used, for example, for the braking force control of the front axle or front axle group, and the second channel can be used for the braking pressure control of the rear axle or the rear axle group.
According to a further development of the invention, a control unit is provided for the plausibility check of the rotational wheel speed signals supplied by the rotational wheel speed sensors. The rotational wheel speed signals are checked particularly with respect to “signal peaks” which are based on interference. In the control unit, an analyzing algorithm is implemented which recognizes “faulty” rotational wheel speed signals and optionally excludes them for calculating the reference speed. All detected rotational wheel speed signals can be analyzed in a common arithmetic unit, can be compared with one another and can be checked with respect to plausibility. This permits the detection of “implausible” or “disturbed” rotational wheel speed signals and therefore increases the safety of the entire braking system.
The invention can be implemented at very reasonable cost because only one arithmetic unit or only one brake control unit is required. It can be used in the case of passenger cars, trucks, motor bikes as well as in the case of rail vehicles or trains.
These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.